Nonlinear receiver compression effects on the amplitude distribution of backscattered ultrasonic signals

Nonlinear receiver compression effects on the amplitude distribution of backscattered ultrasonic signals were investigated using digitized RF signals compressed using an ultrasonic B-scan imaging instrument. Amplitude distributions of compressed RF and video signals were obtained from regions of B-scan images that approximately correspond to the same physical region in a random medium model with known backscatter amplitude characteristics. The amplitude distribution of the signal before compression was obtained by using a table constructed from measurements of the imaging instrument compression characteristics as a function of time gain compensation. While the results indicate the general form of the decompressed data agrees with single-parameter-model curves predicted by a widely used Gaussian random process model, the signal-to-noise ratios of the decompressed envelope vary by up to 20% from the value predicted by that model. This implies that effects such as nonlinearities, envelope smoothing, and noise can cause appreciable departures from theoretical data even under highly controlled conditions.